Low powered training cartridges are known, and examples of such cartridges are disclosed in PCTGB98/00620, PCT/GB99/02859, PCT/GB99/02556, GB 9819928.4 and U.S. Pat. No. 5,492,063. Training cartridges are characterized in that they impart much less energy to a projectile than a live (“killing”) round. Thus, whereas a live round may impart 800 ft/lbs of energy to a bullet and a shotgun may impart as much as 1000 ft/lbs of energy to the shot, training cartridges are much less energetic. For example, the energy imparted to a projectile by a training cartridge is typically less than 5 ft/lbs and more usually less than 4 ft/lbs. The term “training cartridges” as used herein therefore refers to such low energy cartridges, unless the context indicates otherwise.
The aforementioned training cartridges typically contain only a primer and do not contain a conventional amount of propellant. Consequently, they must be carefully designed to ensure that there is sufficient energy both to recycle a weapon and eject a projectile such as a bullet. Many training cartridges, see for example the cartridges disclosed in the patent documents supra, are of the expanding type in which the body of the cartridge comprises a “piston and cylinder” arrangement. With such cartridges, part of the energy of the primer is used to force the piston and cylinder apart (i.e. expand the cartridge) and drive the rear end of the cartridge back to recycle the weapon, and part of the energy is used to discharge the projectile from the front end of the cartridge. Careful control of gas flow within the cartridge is required in order to make sure that the projectile is discharged at a consistent and appropriate velocity and that the weapon is recycled at every firing.
All (so far as the Applicants are aware) current training ammunition, and most live military ammunition, is of the centre fire variety. Exceptions are certain 0.22″ (5.56 mm) rounds generally used in target shooting (and occasionally in military training) which are of the rimfire type. Live cartridges of the centre fire variety generally have a primer carried in a cup or “can” set into the rear end of the cartridge. However, with live rounds of the rim fire type (for example the 0.22″ rounds referred to above) the primer is not carried in a cup or can but is held in the hollow rim of the cartridge case itself.
FIG. 1 shows a sectional elevation through the primer for a centre fire cartridge of the type typically used in live military ammunition. The primer comprises a can 2 formed from, for example, nickel plated brass, and containing a suitable pyrotechnic primer material 4. The can is held in a recess in the centre of the rear surface (not shown) of the cartridge. An anvil 6 is set into the front of the can 2 to close the can and retain the primer in place. As the anvil is inserted into the can, the protruding central part 6a of the anvil greatly compresses the primer to create a compressed region 4a which is highly sensitive to shock. The region 4a which is sensitive to shock has an approximate width I, and this represents the impact area for the firing pin of a centre fire weapon. Thus, a centre fire firing pin will impact against the impact area and further compress the primer between the wall of the can and the anvil thereby detonating the primer. However, it will be appreciated that the firing pin of a rimfire weapon would impact against the can outside the impact area I and hence would not detonate the primer.
Although training cartridges that are constructed to provide consistent low energy discharge of bullets are generally safe per se, safety problems can arise when live killing cartridges are inadvertently mixed with or substituted for low powered training cartridges. As stated above, all of the known existing training cartridges use centre fire type of primers which are very similar and often identical to the types of primers used in the equivalent live killing cartridge for a particular gun type. Attempts have been made to prevent confusion between the two types of cartridge by modifying the gun so that it will not fire the cartridge type usually fired from the gun, but will only fire a training cartridge. Unfortunately, this safety feature can sometimes be bypassed by using a different live cartridge type which, when chambered, fits the gun, or by using damaged live cartridges. In such circumstances, firing live cartridges rather than training cartridges can result in serious injury or death.
It is an object of the present invention to provide a solution to the aforementioned problems by preventing live killing cartridges from being fired inadvertently in place of training cartridges.